<HTML><HEAD><TITLE>rationalize(+Number, -Result)</TITLE>
</HEAD><BODY>[ <A HREF="index.html">Arithmetic</A> | <A HREF="../../index.html">Reference Manual</A> | <A HREF="../../fullindex.html">Alphabetic Index</A> ]
<H1>rationalize(+Number, -Result)</H1>
Converts Number into a compact rational number and unifies it with Result.


<DL>
<DT><EM>Number</EM></DT>
<DD>A number.
</DD>
<DT><EM>Result</EM></DT>
<DD>A variable or rational number.
</DD>
</DL>
<H2>Description</H2>
   This predicate is used by the ECLiPSe compiler to expand evaluable
   arithmetic expressions.  So the call to rationalize(Number, Result) is
   equivalent to
<PRE>
    Result is rationalize(Number)
</PRE>
    which should be preferred.
<P>
   When Number is an integer, Result is a rational with denominator 1.
<P>
   When Number is already a rational, Result is identical to Number.
<P>
   When Number is a float, Result is a rational whose value approximates
   the value of the float to the accuracy of the float representation.
   rationalize/2 usually produces more compact rationals that rational/2.
   Both rationalize/2 and rational/2 produce results that convert back into
   the original float. rational/2 is usually faster than rationalize/2.
<P>
   Bounded reals cannot be converted to rationals.
<P>
   In coroutining mode, if Number is uninstantiated, the call to
   rationalize/2 is delayed until this variable is instantiated.

<H3>Modes and Determinism</H3><UL>
<LI>rationalize(+, -) is det
</UL>
<H3>Exceptions</H3>
<DL>
<DT><EM>(4) instantiation fault </EM>
<DD>Number is not instantiated (non-coroutining mode only).
<DT><EM>(24) number expected </EM>
<DD>Number is not of a numeric type.
<DT><EM>(141) unimplemented functionality </EM>
<DD>Number is a bounded real
</DL>
<H2>Examples</H2>
<PRE>
Success:
      rationalize(25, 25_1).
      rationalize(1.5, 3_2).
      rationalize(3_4,3_4).
      rationalize(9_12,3_4).
      rationalize(-6, Result).      (gives Result = -6_1)
      rationalize(0.1, Result).     (gives Result = 1_10)
Fail:
      rationalize(1, 2_1).
      rationalize(3, 3).
      rationalize(1, r).
Error:
      rationalize(A, 1_3).                   (Error 4).
      rationalize(4 + 2, 6_1).               (Error 24).
      rationalize(0.9__1.1, X).              (Error 141).



</PRE>
<H2>See Also</H2>
<A HREF="../../kernel/arithmetic/rational-2.html">rational / 2</A>, <A HREF="../../kernel/arithmetic/is-2.html">is / 2</A>
</BODY></HTML>
